Difference in Pollen Donor Composition During the Early Phases of Reproduction as Revealed by DNA Analysis of Pollen Grains and Seeds in the Monoecious Tree Castanea crenata

Abstract

In plants, pollen donor composition can differ during the early phases of reproduction through various selection mechanisms favoring self-pollen, related-pollen, or nonrelated-pollen donors, but such differences have not been examined under natural conditions because paternity is difficult to analyze in a natural setting. Therefore, we performed paternity analyses based on the relatively simple technique of microsatellite genotyping by amplifying the DNA from individual pollen grains deposited on female flowers and seeds to evaluate pollen donor composition from three individual trees of the insect-pollinated monoecious tree Castanea crenata in a natural forest. Spatial genetic structure was also investigated. A mean self-pollen rate of 90.2% was observed at the pollination stage, but a low selfing rate of 0.3% was observed at the seed stage. In outcross events, however, pairwise distance and relatedness between maternal and paternal parents were not different between the pollination and seed stages. In our natural population, we observed significant positive relatedness, based on clear fine-scale genetic structure, of individual trees within 80 m of one another, and 71% of the seeds were derived using pollen grains of related trees within 80 m. The results suggest that the mechanism of self-incompatibility strongly avoids self-pollen before seed production. On the other hand, the avoidance of biparental inbreeding was not obvious between the pollination and seed stages.

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